The frame of a wheelchair consists of two collateral frame sections which are each formed from pipe or tubular material and which are connected to each other via a cross beam. A fitting is inserted in each of the collateral frame sections, into which a rear wheel (drive gear) can be screwed with its axle. In order to improve the maneuverability and turning radius of the wheelchair, the wheel axles may not be arranged vertically (0° camber), but at an angle, so that the wheels are inclined from the vertical toward each other and assume a positive camber. The fitting is inserted into the collateral frame section diagonal to the angle forced by the camber angle using the support plates.
In order to be able to adjust the wheelchair to the individual requirements of the user, among other things the seat angle must be able to be changed. In the currently described wheelchair, the seat is rigidly connected to the collateral frame sections and the cross beams, so that an incline position can only be achieved if the frame is tilted, which can be done using wheels with a greater or smaller diameter or though attaching the wheels to the frame at a different height. If rear wheels with a smaller diameter are used, the frame will tilt backward in accordance with the smaller diameter and the seat tilts accordingly.
Through the tilt movement of the frame, the position of the longitudinal axis of the fittings changes as well as the position of the wheel axles and the camber lead to changing the track. The distance between the rear wheels is then greater or smaller in front of the axle than behind it. With the change of the track, the performance of the wheelchair will change. A tendency to wobble and increased tire wear are the results.
From DE 37 42 547 A1, a sport wheelchair is known, on which the collateral frame is equipped with protruding perforated plates for support of the axles for the rear wheels, for which the perforated plates are positioned to be able to pivot around an axle.
DE 296 05 439 U1 publishes a wheelchair with an undercarriage frame which consists of two collateral frame sections each with an upper and lower frame section, each being able to have a perforated plate to support and store a secure yet removable anchor for a wheel axle in the hub of the drive gear.
From GB 2 128 143 A, a wheelchair is known whose frame is made up of a bearing block, which has a number of bearing bores, in order to adjust the wheels selectively on various horizontal and/or vertical levels.
Starting from this problem, the wheelchair described at the beginning should be improved, so that the track of the rear wheels is adjustable.